The present invention generally relates to friction welding and, more particularly, to a portable friction forge welder for welding first and second workpieces together that applies direct axial load to the workpieces via a rotating stored energy linear axial actuator placed between the workpieces and a rotational device.
Friction welding is a process that welds metal or thermoplastics in which two members are joined by rubbing the mated parts under pressure. Heat is generated by direct conversion of mechanical energy to thermal energy at the interface of the mated parts, without the application of electrical energy or heat from other sources. The weld is made by holding a non-rotating part in contact with a rotating one under constant or gradually decreasing pressure, until the interface reaches a certain temperature, for example, forging temperature for metal parts. Rotation is then automatically stopped for a short period of time to consolidate the weld. Weld time varies depending on the materials being joined and the diameter of the workpiece to be joined.
Many industries have need for an effective portable friction forge welder for in situ or job site use. For example, within the petrochemical industry there are many systems directing the flow of fluids or gases through pipelines and valves which control the flow of those fluids and gases that often need to be replaced, repaired, or repacked in situ in the field. Due to the potentially flammable or explosive nature of such environments, traditional fusion welding methods are not utilized while the system is in a “live” on line status. Typically, in the field a drill and tap technique is used to join workpieces to repair such pipelines and valves. A drill initially bores a hole into a second workpiece and the bored hole is tapped or threaded. A threaded first workpiece, for example, a fitting is then able to be joined to the second workpiece. However, because of the inherent weakness of threaded connections and the potential leaks inherent in a non-sealed threaded connection, this practice is often considered to be an “emergency fix” to accommodate a temporary online repair of installation that will be replaced with a more permanent repair or replacement during scheduled shutdown repair or maintenance periods. Implementation of a repair during online conditions utilizing a friction forge welded component eliminates this risk of leakage and provides an acceptable permanent solution.
It is well established that portable friction forge welding is well suited for use in flame and spark restricted environments, such as those common to underground mines, petrochemical plants, refineries and off-shore oil drilling platforms. In such restricted or potentially explosive environments the preferred power source for tools is “non-electric” and is generally air-based (pneumatic). For reasons of safety in potentially explosive environments, conventional portable friction welders typically rely on available industrial pneumatic power sources of approximately 90-120 psi @ 65-90 CFM. Limited by this source to provide power to portable friction welders, conventional portable friction welders normally share this common pressurized air supply for producing rotational torque and axial force. This is, existing pneumatically powered portable friction welders, designed for in situ stud welding of workpieces (for example, attaching threaded studs or bosses to a second work piece) and similar applications utilize an integrated mechanism to apply both the necessary rotational force using a motor to apply torque & rpm and the necessary axial force using a linear actuator to apply axial forging force concurrently from a typically available industrial air supply.
This single shared motor power source limits the combined power capability of the welder. As a result, relatively high rpm and low torque pneumatic motors have been used because they minimize use of the compressed air supply and allow the remaining available energy of the air supply to be used to apply and maintain the necessary axial forging force required for friction welding. In a typical operational sequence of a conventional portable friction welder, the high RPM, low torque motor is allowed to reach a maximum rotational speed prior to applying an axial force, and the motor is typically forced to a much lower rotational speed or stalled condition as the axial force is applied.
Because of the limitations of the shared motor, these integrated “shared pneumatic power” designs limit the maximum workpiece or stud diameter that can be effectively welded to below ¾ in diameter. Additionally, the use of high rpm motors may generate higher than necessary temperatures that may also lead to undesirable weld characteristics. Fluctuations in the air supply may result in less than desirable forging force being applied. Furthermore, existing portable friction welder designs require a relatively complex control sequence so that when full rotational speed (rpm) is started and achieve, an integrated linear actuates is charged, either all at once or through sensing components, and the actuator applies and maintains the forging force following cessation of rotation until bonding is achieved.
A portable friction forge welder applying direct axial load to the workpieces via a rotating variable pressure means placed between the workpieces and a rotational device would be an improvement over the current arc welders, current portable friction welders and stationary friction welders because such a portable friction forge welder would enable a user to carry the portable friction forge welder on site and operate on live systems, and the rotational device would be totally independent of the pressurizing device. Such a portable friction forge welder should be able to effectively weld fittings in excess of one inch diameter, which is a substantial gain over the current art, and should also allow welded work to be contained and purged.
Therefore, a need exists for a portable friction forge welder which welds workpieces together with sufficient force to provide sufficient weld strengths, eliminates potential fluid or gas leaks resulting from online repairs and installation, prevents the surface temperature of the workpiece portion in contact with flammable materials from reaching undesirable temperatures, and provides a simple and effective means to accomplish these goals using a variety of workpiece materials, shapes, configurations and size.